In a cellular or mobile telecommunications network, each base station (BS) corresponds to a respective cell of the cellular or mobile telecommunications network and receives calls from and transmits calls to a mobile terminal in that cell by wireless radio communication. Such a subscriber's mobile terminal is shown at 1 in FIG. 1. The mobile terminal may be a handheld mobile telephone, a personal digital assistance (PDA) or a laptop computer equipped with a datacard.
Key elements of a Long Term Evolution (LTE) network are shown in FIG. 1. The base stations 2, 3 and 5 comprise an eNodeB (evolved Node B, eNB) 7. The RRC signalling with the mobile terminal 1 terminates at the eNodeB 7, the eNode B comprising the Radio Access Network (RAN) of the LTE network. The eNodeB 7 performs the functions of both the Node B and a large part of the RNC of a 3G/UMTS network. The network core 11 of the LTE network includes Serving Gateway (S-GW) 13, Packet Data Network Gateway (PDN-GW) 15, the HLR/HSS 17 (e.g. a common HLR/HSS shared with the network core of a GSM/UMTS network) and also Mobility Management Entity (MME) 19. A plurality of PDN-GWs are usually provided, although only one is shown. The LTE network communicates with an external packet data network PDN 21.
The LTE physical layer is based on Orthogonal Frequency Division Multiplexing scheme (OFDM) to meet the targets of high data rate and improved spectral efficiency.
The spectral resources are allocated/used as a combination of both time (“slot”) and frequency units (“subcarrier”). The smallest unit of allocation is a subframe of two slots corresponding to two resource blocks (RBs). A resource block is 12 sub-carriers for a half a sub-frame (0.5 ms).
For LTE there needs to be a method to allow neighbouring cells to co-exist, and this requires the common radio resource blocks that interfere to be shared in a “soft” manner between neighbouring cells. The soft sharing is not measured by number of resource blocks which is used in the system, but by the amount of interference that can be introduced into the neighbour cell for each of the resource blocks.
If a cell detects too much interference in the uplink, it has been proposed that an overload indication is passed between eNodeBs controlling neighbour cells, allowing them to inform each other that they are injecting too much interference (Rise Over Thermal) on a specific resource.
These known proposals are directed to congestion situations, and do not allow the system to intelligently adapt for the non-uniform distributions of UEs in the coverage area of a particular eNB, as in the known arrangement the radio resources would need to be co-ordinated between neighbouring cells in proportion to the amount of UEs registered with or camped on each eNB, and neither does the known arrangement address differential QoS requirements of neighbouring cells.
It has been a broad design assumption that when the eNB has data to transmit on a sub-carrier it would transmit on the sub-carrier at a constant Maximum power. Each sub carrier would be configured with a Maximum power, and the value could vary between sub-carriers. For the centre 1.25 MHz of the carrier the eNB would need to maintain its transmit power as this is what UEs will be making measurements of, and using these measurements to determine whether to select and reselect to/from this cell, so these need to be constant.
Accordingly, it would be desirable to provide an improved arrangement of reducing interference.